Pumps for dosing fluids are required in a number of technical contexts. In certain of these technical contexts, it is desirable for the dose provided by the pump to be controllable with great accuracy, and for one pump to provide very similar dosing outputs to another pump according to the same design. One such technical context is the dosing of urea solution into the exhaust system of an internal combustion engine to allow a selective catalytic reduction (SCR) catalyst to reduce oxides of nitrogen. A dosing system for this purpose is described in EP1878920.
In practice, it is difficult to achieve very high levels of dosing control together with very high levels of consistency in dosing performance between different pumps manufactured according to the same design. It is desirable to address this difficulty without increasing complexity and cost in the manufacturing process.